Hurricane FERNANDA

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Hurricane Fernanda Discussion Number 13
NWS National Hurricane Center Miami FL EP062017
800 PM PDT Fri Jul 14 2017
Fernanda continues to have a very impressive appearance in
satellite imagery, with a 10 n mi wide eye well embedded in a
symmetric central dense overcast. The hurricane also has good
outflow in all directions and outer convective bands in all
quadrants except the northwest. Subjective satellite intensity
estimates from TAFB and SAB are now 127 kt, and recent estimates
from the CIMSS Advanced Dvorak Technique are now 120 kt. Based
mainly on these data, the initial intensity is increased to 125 kt.
The initial motion is now 270/10. The track forecast philosophy
remains the same as earlier, as a mid-level subtropical ridge to
the north of Fernanda should induce a generally west-northwestward
track for the next several days. Some decrease in forward speed is
likely late in the forecast period when the tropical cyclone nears a
weakness in the ridge. The new track forecast is almost identical
to the previous forecast and lies near the various consensus models.
Recent microwave imagery indicates rainbands about 30-40 n mi from
the center that are likely the start of an outer eyewall and an
eyewall replacement cycle that will end the current
intensification. The new intensity forecast allows for 6-12 h more
strengthening before this happens. From 12-48 h, Fernanda should
remain in a low shear environment over very warm sea surface
temperatures. The intensity forecast calls for a slow weakening
during this time as a reflection of the guidance. However,
fluctuations in intensity caused by eyewall cycles are likely to
occur, and it would not be surprising if a second round of
strengthening occurs if a cycle can finish before Fernanda leaves
the very warm water. After 48 h, the hurricane will move over
decreasing sea surface temperatures, and this should result in a
steady weakening. Overall, the new intensity forecast lies at or
above the upper edge of the intensity guidance.
FORECAST POSITIONS AND MAX WINDS
INIT 15/0300Z 10.7N 120.8W 125 KT 145 MPH
12H 15/1200Z 11.0N 122.5W 135 KT 155 MPH
24H 16/0000Z 11.6N 124.9W 130 KT 150 MPH
36H 16/1200Z 12.2N 127.3W 130 KT 150 MPH
48H 17/0000Z 12.8N 129.5W 125 KT 145 MPH
72H 18/0000Z 14.5N 133.5W 105 KT 120 MPH
96H 19/0000Z 16.0N 137.0W 80 KT 90 MPH
120H 20/0000Z 17.0N 140.0W 60 KT 70 MPH
$$
Forecaster Beven
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